Grid member and wall formed therefrom

ABSTRACT

A grid member for supporting packings in liquid-gas contact apparatus is molded in one-piece of synthetic plastic material. The grid member is rectangular and has spaced-apart intersecting ribs which provide high-structural strength with a minimum of plastic material. The grid member includes interlocking projections extending outwardly from a pair of opposite side edges. A plurality of the grid members are assembled into a perforate grid supporting wall for supporting packings in liquidgas contact apparatus.

United States atom Klugman 2 7 9 n 9 2 to w W H H 3,118,957 1/1964 Yerzley....... 3,324,630 6/1967 Tellereta [54] GRID MEMBER AND WALL FGRMIED THEREIFR'OM Warren Lrlliiugman, Middleburg Heights, Ohio [72] Inventor:

.52/664 454,677 2/1949 Canada................ ....209/393 [73] Assignee: Ceilcote Company, Bcrea, Ohio [22] Filed: Mar. 4, 1970 ........52/664 Switzerland 396,848 8/1933 GreatBritain... 383,338 12/1964 [21] Appl.No.:

Primary Examiner-Tim R. Miles Attorney-Meyer, Tilberry and Body [51] lnt.Cl. 3/041 57 ABMRACT [58] Field ofSearch...............,.....................261/9498, 112; I

52/664 209/393; 5 5 [233 A grid member for supporting paclungs in liquid-gas contact apparatus is molded in one-piece of synthetic plastic material. The grid member is rectangular and has spaced-apart inter- [56] References Cited UNITED STATES PAT secting ribs which provide high-structural strength with a minimum of plastic material. The grid member includes inter- ENTS locking projections extending outwardly from a pair of opposite side edges. A plurality of the grid members are assem- 3'189'335 6,1965 bled into a perforate grid supporting wall for supporting 2,128,753 8/1938 Lleqhard packings in liquid-gas contact apparatus. 2,162,742 6/1939 Nagin........ 3,222,040 12/1965 Eckert 6 Claims, 13 Drawing Figures Patented Feb. 29, 1972 3,645,510

V5. INVENTOR. f ll MRREN L. KLUGMAN MW W m A TTOR/VEYS Patented Feb. 29, 1972 5 Sheets-Sheet 5 INVENTOR. WA REE/V L KLUGMA/V www fmy ATTORNEYS Patented Feb. 29, 1972 5 Sheets-Sheet L w w s k H- H m w w w H a a? G M vkmfwilrlgairvILLEL: W fl n K W W M. m m M m k MH W HIM W n ...H J J l i 4 2 Ea g w w w a w ATTORNEYS Patented Feb. 29, 1972 3,645,510

5 Sheets-Sheet 5 v INVENTOK WAR/PE N L. KLUGMAN ATTORNEYS GRID MEMBER AND WALL FGIIMEII THIERIEFROM BACKGROUND OF THE INVENTION This application pertains to the art of structural grid members and more particularly to structural grid members through which gas and liquid flow. The invention is particularly applicable to packing support grids and grid wall assemblies used in liquid-gas contact apparatus and will be described with particular reference thereto although it will be appreciated that the invention has broader applications and may be used in other environments.

Air pollutants commonly occuring in industrial areas include the following: noxious gases which normally exist in a vapor state such as chlorine or sulpher dioxide; liquid entrainment such as large size liquid particles created by sprays or bubbling; mists in the form of liquid particles resulting from condensation of molecules from the vapor state such as sulphuric acid vapor condensing to sulphuric acid mist; dusts of solid particles formed by grinding or disintegration of solid materials; fumes of solid particles formed by condensation, sublimation, or oxidation of metalic vapors such as zinc oxide fumes; and entrained particles of mists, liquids, dusts or fumes which are conveyed in an airstream through an exhaust ventilation system. Pollutants of the type described are commonly removed from an airstream through a liquid-gas contact apparatus. Such apparatus is commonly referred to as an air scrubber and includes a large receptacle containing packing such as the type described in US. Pat. No. 2,867,425, to Teller. Water or other liquid is sprayed on the packing and allowed to flow over it. Pollutants of the type described are absorbed or diffused into the liquid as the airstream passes through and around the packing which is wetted by the liquid. Packing elements for use in such liquid-gas contact apparatus may be in the form of ceramic cylinders or saddles, or special shapes of synthetic plastic material as described in the beforementioned Teller patent. Such packing elements must be supported by an open grid through which the airstream may freely flow. It is desirable that the grid support be formed of a noncorrosive material so that it will not rapidly deteriorate when contacted by pollutants in the airstream. It is also desirable that the grid support itself will not rapidly clog due to a bulldup of pollutants thereon. In previous apparatus, grid supports for packing elements were specially constructed for each liquid-gas contact apparatus and were often of corrosive metal mesh or wire.

SUMMARY OF THE INVENTION In accordance with the present invention, a grid support for use in liquid-gas contact apparatus of the type described is defined by a rectangular grid member molded in one-piece of synthetic plastic material. In accordance with a preferred arrangement, a rectangular grid member has a first pair of parallel spaced-apart side flanges and a second pair of parallel spaced-apart side flanges perpendicular to the first pair. The flanges encompass a rectangular grid defining area and a first plurality of parallel spaced-apart ribs extend across the first pair of flanges. A second plurality of parallel spaced-apart ribs extend across the second pair of flanges and intersect the first ribs at a plurality of spaced-apart intersection points throughout the grid defining area. The first and second ribs encompass a plurality of rectangular grid openings within their intersection points. The grid member has first and second opposite faces with the flanges and ribs all having first edges lying in a common plane at the first face. With this arrangement, the first face of the grid member is completely smooth. The second face of the grid member is recessed and defines somewhat of a basket. This is accomplished by having the second edges of the flanges and ribs spaced varying distances toward the second face from the plane of the first face. In a preferred arrangement, a certain minor number of the first and second ribs are structurally larger than a majority of such ribs to improve the structural strength of the grid member. The grid member also includes a plurality of spaced-apart projections extending outwardly from one of the pair of opposite flanges. The projections include recessed upper and lower edges which may be positioned on a support member for supporting the entire grid member. In a preferred arrangement, the projections further include lateral extentions which help to interlock a pair of grid members or allow a pair of grid members to be abutted on a common support without shifting. The second ribs are preferably smaller than the first ribs so that they may be positioned horizontally in a wall formed from a plurality of the grid members. Positioning the smaller ribs horizontally substantially eliminates any problem with buildup of pollutant material on horizontal ribs.

In accordance with one arrangement, a substantially vertical perforate grid wall may be formed by utilizing parallel channel members having open channel portions facing one another. A plurality of grid members formed in accordance with the present invention have opposite side edges thereof received in the channels. In a preferred arrangement, intermediate channel members for forming such a perforate grid wall are substantially F-shaped so as to leave leg portions which may be secured to one another.

It is a principal object of the present invention to provide an improved grid member for use in liquid-gas contact apparatus.

It is also an object of the present invention to provide an improved grid member which achieves a high structural strength while utilizing a minimum of material.

It is a further object of the present invention to provide an improved grid member which is more economical to manufacture and to assemble in a liquid-gas contact apparatus.

It is an additional object of the present invention to provide a grid member having enhanced self-cleaning properties.

It is a further object of the present invention to provide an improved perforate grid supporting wall assembly for use in liquid-gas contact apparatus.

BRIEF DESCRIPTION OF THE DRAWING The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawing which forms a part hereof.

FIG. I is a perspective view looking down on the bottom face of the improved grid member of the present invention;

FIG. 2 is a partial elevational view looking in the direction of arrows 2-2 of FIG. I;

FIG. 3 is a cross-sectional elevational view looking in the direction of arrows 33 of FIG. 1;

FIG. 4 is a cross-sectional elevational view looking in the direction of arrows 4-4. of FIG. 1;

FIG. 5 is a cross-sectional elevational view looking in the direction of arrows 55 of FIG. I;

FIG. 6 is a cross'sectional elevational view looking in the direction of arrows 6-6 of FIG. I;

FIG. 7 is a partial cross-sectional elevational view showing end portions of a pair of grid members constructed in accordance with FIG. I resting on a common support;

FIG. 8 is a top plan view looking in the direction of arrows 8-3 of FIG. 7;

FIG. 9 is a partial cross-sectional elevational view showing edge portions of a pair of grid members interdigitated and resting on a common support;

FIG. I0 is a top plan view looking in the direction of arrows III-I0 of FIG. 9;

FIG. II is a cross-sectional elevational view showing a liquid-gas contact apparatus having an improved supporting grid wall assembly utilizing the grid member of FIG. I;

FIG. I2 is a top plan view looking in the direction of arrows 12-12 of FIG. II; and

FIG. I3 is a side elevational view looking in the direction of arrows Iii-I3 of FIG. I2.

DESCRIPTION OF THE PREFERRED EMBDDIMENT Referring now to the drawings wherein the showings are for purposes of illustrating the preferred embodiment of the invention only and not for purposes of limiting same, FIG. 1 shows a molded one-piece rectangular grid member A. Grid member A includes first and second spaced-apart parallel side flanges 12 and 14; and third and fourth spaced-apart parallel side flanges l6 and 18 perpendicular to side flange 12 and 14. A first plurality of parallel spaced-apart ribs, only one of which is referenced by numeral 20 in FIG. 1, extend across first and second side flanges 12 and 14. A second plurality of parallel spaced-apart ribs, only one of which is referenced by numeral 22 in FIG. I, extend across third and fourth flanges l6 and 18. It will be recognized that side flanges 1243 encompass a grid defining area in which ribs 21) and 22 are located. First and second ribs 20 and 22 intersect one another at a plurality of spaced-apart intersection points throughout the grid defining area encompassed by side flanges 12-18, and only one of such intersection points is referenced by numeral 24 in FIG. 1. Intersection points 24 lie at the corners of rectangles, and first and second ribs 20 and 22 cooperate to define rectangular grid openings within each four intersection points, only one such grid opening being referenced by numeral 26 in FIG. 1. It will be recognized that first ribs 20 also intersect first and second side flanges 12 and 14 as at intersection points 28 and 30. Second ribs 22 also intersect third and fourth flanges l6 and 18 as at intersection points 31 and 33, respectively.

In a preferred arrangement, as shown in FIG. 3, grid member A has a bottom first face defined by a plane 34 and a front second face defined by plane 36. Side flange 12 has a first edge 38 lying in plane 34 and it will be recognized that side flanges 14, 16 and 18 also have first edges lying in a common plane, defined by plane 34, with first edge 38 of flange l2. Ribs 20 include first edges 40 while ribs 22 include first edges 42. First edges 40 and 42 of ribs 20 and 22 also lie in a common plane defined by plane 34. Side flange 12 has a second edge 44 lying in plane 36 and it will be recognized that side flanges 14, 16 and 18 have corresponding second edges lying in plane 36. Therefore, it will be recognized that all of side flanges 12-18, and ribs 20 and 22, have first edges lying in a common plane defined by plane 34. Flanges 12-13 also have second edges all lying in a first plane 36 at the front second face of grid member A. As best shown in FIG. 3, first plane 36 is spaced a first distance 46 from common plane 34. Ribs 20 also have second edges 48 lying in a common second plane 50. Second plane 50 is spaced a second distance 52 from common plane 34 with second distance 52 being substantially less than first distance 46. Second ribs 22 also have second edges 54 lying in a common third plane 56 which is spaced a third distance 58 from common plane 34,-. Third distance 58 is substantially less than second distance 52. While all of ribs 20 and 22 may have edge spacings as described, a preferred arrangement provides only a substantial majority of ribs 211 and 22 with such spacings while a substantial minority of such ribs, located in predetermined positions, are heavier to enhance the structural properties of the grid. For example, second ribs 22 include a pair of ribs 22a having first edges 42a which lie in common plane 34 and second edges 54!; which lie in second plane 50. in addition to a minor number of stronger ribs 22a, second ribs 22 include a centrally located rib 22b having first edge 42b lying in common plane 34 and second edge 54b lying in first plane 36. It will be recognized that centrally located rib 22b has the same dimensions as side flanges 12-18. In the arrangement shown, second ribs 22 total 17 in number. The fourth ribs 22a spaced inwardly from each of side flanges 12 and 14 are larger than the majority of ribs 22 while central rib 22b is even larger and of substantially the same dimensions as side flanges 12-18. With this arrangement, grid member A is structurally very strong and is capable of supporting a large number of packings without bending or breaking.

In addition to certain of second ribs 22 being stronger than other, certain of first ribs 20 are also stronger. in accordance with one arrangement, the fourth ribs 20:: and 211s spaced inward from side flanges 16 and 18 are of the same dimensions as side flanges 12-18. As shown in H6. 5, enlarged ribs 20b and 2130 include first edges 40b and 411C lying in common plane 34, and second edges 48b and 480 lying in first plane 36. Enlarged rib 20a has corresponding first and second edges lying in the same plane. In the arrangement shown and described, there are 15 of first ribs 20, and three of such ribs 20a, 20b and 200 are larger than the others. Therefore, a substantial majority of first ribs 20 are of the same size while a substantial minority are structurally larger. In a preferred arrangement, the smaller ribs slope upwardly at their intersection points with larger ribs or with the side flanges. For example, ribs 20 slope upwardly as at 62 out of second plane 50 toward the second face of grid member A as defined by first plane 36 in FIG. 3. Rib 42 slopes upwardly as at 64 and 66 at its intersection with enlarged ribs 20b and 200. As shown in FIG. 6, small second ribs 22 slope upwardly as at 68 and 70 when intersect ing larger ribs 20. This upward sloping of the smaller ribs at the intersection points with larger ribs or flanges increases the stiffness of the grid member while utilizing a minimum of material and presenting a minimal surface area for the major portion of the grid area.

In accordance with the preferred arrangement, side flanges 16 and 18 have a plurality of spaced-apart projections B and C extending outwardly therefrom. Each of projections B and C includes an outwardly extending portion 72 and 74, and laterally extending leg portions 76 and 78. Outwardly extending portions 72 and 74 are located in alignment with second ribs 22. In addition, the spacing between the outer faces of flanges 16 and 18, and the inner faces of lateral leg portions 76 and 78, is the same as the spacing between opposed faces of first rib members 20. Each lateral leg portion 76 and 78 extends perpendicular to outwardly extending portions 72 and 74 toward an adjacent outwardly extending portion, and terminates a predetermined distance therefrom which is greater than the thickness of outwardly extending portions 72 and 74. Two opposite comers of grid member A include outwardly extending portions 72a and 74a which are formed without lateral leg portions. Outwardly extending portions 72a and 74a extend outwardly a slightly greater distance than portions 72 and 74 so that their outer edges lie in the same plane as the outer faces of leg portions 76 and 78. With this arrangement, the outer surfaces of flanges 12 and 14, along with the outer surfaces of leg portions 76 and 78, define a grid member which is square. Since a square is merely a special form of rectangle, it will be understood that grid member A may be formed square as described, or with one opposed pair of flanges 12 and 14, or 16 and 18, longer than the other pair.

In accordance with a preferred arrangement, the upper and lower edges of outwardly extending portions 72 and 74 are recessed as at 80 and 82 so that supporting members for grid A may be positioned in such recesses. In addition, laterally extending leg portions 76 and 78 include terminal edges 84 and 86 which slope inwardly toward outwardly extending portions 72 and 74 in a direction from common plane 34 toward first plane 36 as best shown in FIG. 2. With this sloping arrangement, interdigitating of projections B and C with corresponding projections on an adjacent grid member is more easily accomplished. It will be recognized that lateral leg portions 76 extend from outwardly extending portions 72 toward side flange 12, while lateral legs 78 extend toward side flange 14 from outwardly extending portions 74.

Those skilled in the art will be readily aware that the improved grid member of the present invention is particularly suited for manufacture in one-piece of synthetic plastic material by injection molding procedures. The grid member may be molded of various suitable materials such as linear polyethylene or polypropylene, or polypropylene filled with talc or glass. In addition, the improved grid member of the present invention provides an extremely high structural strength while utilizing a minimum of material. Forming all of the ribs and flanges with first edges lying in a common plane at a first face of the grid member provides a smooth surface which is broken only by the open grid areas, while the second face is stepped. in the preferred arrangement, the thickness of ribs and 22 is such that grid openings 2s define at least 75 percent of the area encompassed within the inner faces of side flanges 12-18. With the arrangement described, two grid members A may be positioned in side-by-side relationship with projections B and C of adjacent grid members supported on upper web 88 of l-beam D. The substantial lateral extent of leg members 76 and 78 allow their outer faces to contact one another and prevent adjacent grid members A from shifting away from one another. In addition, the open area encompassed within two adjacent outwardly extending portions 72 or 74, and a leg portion 76 or 78, is substantially the same as the area of grid openings 26 so that packing elements may be supported on projections B and C when adjacent grid membets are abutted.

While a pair of grid members A are shown abutted in FIGS. 7 and 8 with projections B on one grid member contacting projections C on the adjacent grid member, the design of the projections is such that identical projections B or C on two adjacentgrid members may be positioned in abutting relationship.

In accordance with another arrangement, projections B on one grid member A may be interdigitated with projections C on a second adjacent grid member A as shown in FIGS. 9 and it). Sloping edges 84 and 86 on leg portions 76 and 7 8 assist in positioning leg portions 76 on one grid member between outwardly extending portions 74 on an adjacent grid member. With this arrangement, projections B and C define interlocking means for interlocking adjacent edges of a pair of grid members and also make it possible to support interlocked edges of a pair of grid members on a common support. Leg 92 of T-beam E is received in recesses 80 and 82 when projections B and C are interdigitated. Recesses 80 and 82 limit lateral shifting movement of a pair of adjacent grid members relative to a common support when such support includes a portion which is received in the recesses as shown in FIG. 9.

With the grid member of the present invention, supporting walls for packing elements may be readily constructed in a horizontal, vertical or sloping configuration. In one arrangement, as shown in FIG. ill, a liquid-gas contact apparatus includes a large receptacle H of a known type having an air inlet 102 and an air outlet 104. A suitable blower is provided for forcing air through receptacle H. A pair of supporting walls J and K are positioned within receptacle H and extend completely thereacross from one sidewall to the other thereof. The space between walls I and K is filled with packing ele ments in a known manner. Receptacle l-i includes atop opening 1106 for this purpose and opening 1% is normally closed by a cover during operation of the device. A header pipe 108 is provided with a plurality of spray nozzles ill) opening downwardly for wetting the surfaces of the packing elements located between walls J and K with water or other liquid in a known manner. Suitable baffles, which are of a known type and not shown for simplicity of illustration, may be positioned inside of the top portion of receptacle l-l to force air through both of walls I and K, and the packing elements contained therebetween. The bottom portion of receptacleH is alsopro vided with a separate outlet for liquid in a known manner. In the preferred arrangement, spacedapart opposed sidewalls 114i and H6 of receptacle H have elongated channel members 120 and 122 secured to the inner surfaces thereof. Channels 120 and 122 may be extruded of polyvinyl chloride and may be attached to walls 114 and lid by adhesive. Channels 12th and 122 include open channel portions 124 and 126 which open outwardly and face one another. Elongated intermediate channel members 128 and lllltl, of identical construction, include open channel portions i132 and 1134. Each intermediate channel member 128 and i134) has a substantially F-sh aped cross-sectional shape. Intermediate channel members 128 and 130 may also be extruded of polyvinyl chloride. Each such intermediate channel member H23 and 11% includes a main leg defined by a first portion 1136 and 138 forming the bottom of open channel portions R32 and H34, and a second portion M4 and M2 extending laterally beyond the channel portions. intermediate channel members 123 and. 1134 are positioned with the main legs thereof facing one another and with open channel portions 136 and 13% facing in opposite directions. Verti cally spaced horizontal strut members M of rectangular crosssectional configuration extend from support wall .I to support wall K. Strut members M include end portions positioned between adjacent intermediate channel members Md and I39. Second portions M0 and M2 of the main legs of intermediate channel members Il2b and 1130, along with the end portions of strut M, are provided with suitable holes through which fasteners R50 extend. Fasteners 150 may be of a known type molded of synthetic plastic material and including spaced-apart bifurcated legs having enlarged heads on the ends thereof. The bifurcated legs are bendable toward one another for insertion through the holes provided and spring outwardly so that their enlarged heads lock on one side of a hole while the enlarged head on the other end of the fastener itself abuts an element on the other side of the hole. It will be recognized that the manner of fastening struts M, and intermediate channel members ll28 and 130 together may be accomplished in any desirable manner. Open channel portions 124 and 132 face one another in opposed spaced-apart parallel relationship to define a first guideway while open channel portions 126 and 134 face one another in opposed spacedapart parallel relationship to define a second guideway. A plurality of grid members A, as described with reference to FIGS. llo, have projections B and C received in these guideways with adjacent flanges 12 or 14 on vertically adjacent grid members abutting one another. Perforate grid walls are then provided for supporting packing elements in a desirable configuration and such a perforate supporting grid wall offers little resistance to flow of air therethrough. In addition, any number of pairs of intermediate channel members 128 and 1130 may be provided to extend such a supporting wall completely across a receptacle having opposed sidewalls positioned different distances from one another. With the arrangement described, it will be recognized that larger first ribs Ztl will be vertical when projections B and C are received in the guideways defined by the open channel portions. it is common to provide water spraying against the outside surfaces of perforate grid walls .l and K to wash pollutants of the type described from grid members A. Such water flows downward by gravity and thoroughly cleans larger first ribs 20 to prevent the buildup of pollutants thereon. Smaller second ribs 22, which have a much smaller surface area than ribs 26, are positioned horizontally in walls 1 and K. Due to the smaller surface area of ribs 22, they are less likely to develop a rapid buildup of pollutants than larger first ribs 24}. Therefore, the reduced washing action on horizontal ribs 22 is still sufficient to remove the reduced pollutant buildup thereon. With the grid member of the present invention designed in the manner described, maximum structural strength is provided by the various sized ribs while permitting efficient washing of pollutants therefrom due to the horizontally positionable ribs being substantially smaller than the vertically positionable ribs. it will be recognized that channel members ll2ll and I122 may be defined as first and second end channel members. Open channel portions 132 of intermediate channel members 128 face open channel portions 1124 of first end channel members while open channel portions 234! of intermediate channel members 1130 face open channel portions 126 of second end channel members 122. Grid members A may be positioned in the guideways defined by the open channel portions with either their first faces defined by plane 3 5, or their second faces defined by plane 36, facing inwardly. While walls J and K have been shown in a substantially vertical position, it will be recognized that such walls may be positioned in parallel spaced-apart relationship at an angle to the vertical.

While the invention has been described with reference to a preferred embodiment, it is obvious that modifications and alterations will occur to others skilled in the art upon the reading and understanding of this specification. The present invention includes all such equivalent modifications and alterations and is limited only by the scope of the claims.

Having thus described my invention 1 claim:

1. A perforate grid wall comprising; a pair of elongated spaced-apart parallel first and second end channel members having open channel portions facing one another, a pair of elongated parallel intermediate channel members extending parallel to said end channel members each of said intermediate channel members being substantially F-shaped in cross section and including a main leg and a pair of parallel spaced-apart flanges extending outwardly therefrom to define an open channel portion, said main leg including a first portion definirig a bottom wall of said channel portion and a second portion extending laterally beyond said channel portion, said intermediate channel members being positioned in opposed relationship with said main legs facing one another and said open channel portions thereof opening outwardly in opposite directions, said open channel portion on one of said intermediate channel members facing said open channel portion of said first end channel and cooperating therewith to define a first guideway, said open channel portion on the other of said intermediate channel members facing said open channel portion of said second end channel and cooperating therewith to define a second guideway, fastening means securing said second portions of said main legs of said intermediate channel members together, and a plurality of rectangular perforate grid members having spaced-apart opposite side edges received in said channel portions of said guideways.

2. The perforate grid wall of claim 1 wherein said wall defines a first perforate grid wall and further including a second grid wall substantially identical to said first grid wall positioned in substantially parallel spaced-apart relationship thereto, said second grid wall including intermediate channel members, and strut means interconnecting said intermediate channel members of said first grid wall with said intermediate channel members of said second grid wall.

i 3. A molded rectangular one-piece grid member having a first pair of parallel spaced-apart side flanges and a second pair of parallel spaced-apart side flanges perpendicular to said first pair of side flanges, said flanges encompassing a grid defining area, a first plurality of parallel spaced-apart ribs extending across said first pair of flanges, a second plurality of parallel spaced-apart ribs extending across said second pair of flanges, said first and second n'bs intersecting one another at a plurality of spaced-apart intersection points throughout said grid defining area an encompassing a plurality of rectangular grid openings, said grid member having first and second opposite faces, said flanges and ribs having first edges lying in a common plane at said first face, said flanges having second flange edges spaced a first distance from said common plane and lying in a first plane at said second face, at least a majority of said first ribs having second edges spaced a second distance less than said first distance from said common plane and lying in a second plane at said second face, at least a majority of said second ribs having second edges spaced a third distance less than said second distance from said common plane and lying in a third plane at said second face, each of said majority of said first ribs having a width dimension substantially less than the distance from said common plane to said second plane, a plurality of spaced-apart projections extending outwardly from at least said third and fourth side flanges, said projections including laterally extending portions having edge portions sloping inward from said first face toward said second face.

4. A molded rectangular one-piece grid member having a first pair of parallel spaced-apart side flanges and a second pair of parallel spaced-apart side flanges perpendicular to said first pair of side flanges, said flanges encompassing a griddefining area, a first plurality of parallel spaced-apart ribs extending across said first pair of flanges, a second plurality of parallel spaced-apart ribs extending across said second pair of flanges, said first and second ribs intersecting one another at a plurality of spaced-apart intersection points throughout said grid defining area and encompassing a plurality of rectangular grid openings, said grid member having first and second opposite faces, said flanges and ribs having first edges lying in a common plane at said first face, said flanges having second flange edges spaced a first distance from said common plane and lying in a first plane at said second face, at least a majority of said first ribs having second edges spaced a second distance less than said first distance from said common plane and lying in a second plane at said second face, at least a majority of said second ribs having second edges spaced a third distance less than said second distance from said common plane and lying in a third plane at said second face, each of said majority of said first ribs having a width dimension substantially less than vthe distance from said common plane to said second plane, a plurality of spaced-apart support projections extending outwardly from at least said third and fourth side flanges, said projections having outer edges spaced outwardly from said third and fourth side flanges, and recesses formed in said projections intermediate said outer edges and said third and fourth side flanges, said recesses opening outwardly toward at least one of said first and second opposite faces of said grid member.

5. The grid member of claim 4 wherein said recesses open outwardly toward both of said first and second opposite faces.

6. The grid member of claim 4 and further including lateral extensions projecting laterally from said outer edges of said projections in substantially parallel relationship to said third and fourth side flanges. 

1. A perforate grid wall comprising; a pair of elongated spacedapart parallel first and second end channel members having open channel portions facing one another, a pair of elongated parallel intermediate channel members extending parallel to said end channel members'' each of said intermediate channel members being substantially F-shaped in cross section and including a main leg and a pair of parallel spaced-apart flanges extending outwardly therefrom to define an open channel portion, said main leg including a first portion defining a bottom wall of said channel portion and a second portion extending laterally beyond said channel portion, said intermediate channel members being positioned in opposed relationship with said main legs facing one another and said open channel portions thereof opening outwardly in opposite directions, said open channel portion on one of said intermediate channel members facing said open channel portion of said first end channel and cooperating therewith to define a first guideway, said open channel portion on the other of said intermediate channel members facing said open channel portion of said second end channel and cooperating therewith to define a second guideway, fastening means securing said second portions of said main legs of said intermediate channel members together, and a plurality of rectangular perforate grid members having spacedapart opposite side edges received in said channel portions of said guideways.
 2. The perforate grid wall of claim 1 wherein said wall defines a first perforate grid wall and further including a second grid wall substantially identical to said first grid wall positioned in substantially parallel spaced-apart relationship thereto, said second grid wall including intermediate channel members, and strut means interconnecting said intermediate channel members of said first grid wall with said intermediate channel members of said second grid wall.
 3. A molded rectangular one-piece grid member having a first pair of parallel spaced-apart side flanges and a second pair of parallel spaced-apart side flanges perpendicular to said first pair of side flanges, said flanges encompassing a grid defining area, a first plurality of parallel spaced-apart ribs extending across said first pair of flanges, a second plurality of parallel spaced-apart ribs extending across said second pair of flanges, said first and second ribs intersecting one another at a plurality of spaced-apart intersection points throughout said grid defining area an encompassing a plurality of rectangular grid openings, said grid member having first and second opposite faces, said flanges and ribs having first edges lying in a common plane at said first face, said flanges having second flange edges spaced a first distance from said common plane and lying in a first plane at said second face, at least a majority of said first ribs having second edges spaced a second distance less than said first distance from said common plane and lying in a second plane at said second face, at least a majority of said second ribs having second edges spaced a third distance less than said second distance from said common plane and lying in a third plane at said second face, each of said majority of said first ribs having a width dimension substantially less than the distance from said common plane to said second plane, a plurality of spaced-apart projections extending outwardly from at least said third and fourth side flanges, said projections including laterally extending portions having edge portions sloping inward from said first face toward said second face.
 4. A molded rectangular one-piece grid member having a first pair of parallel spaced-apart side flanges and a second pair of parallel spaced-apart side flanges perpendicular to said first pair of side flanges, said flanges encompassing a grid-defining area, a first plurality of parallel spaced-apart ribs extending across said first pair of flanges, a second plurality of parallel spaced-apart ribs extending across said second pair of flanges, said first and second ribs intersecting one another at a plurality of spaced-apart intersection points throughout said grid defining area and encompassing a plurality of rectangular grid openings, said grid member having first and second opposite faces, said flanges and ribs having first edges lying in a common plane at said first face, said flanges having second flange edges spaced a first distance from said common plane and lying in a first plane at said second face, at least a majority of said first ribs having second edges spaced a second distance less than said first distance from said common plane and lying in a second plane at said second face, at least a majority of said second ribs having second edges spaced a third distance less than said second distance frOm said common plane and lying in a third plane at said second face, each of said majority of said first ribs having a width dimension substantially less than the distance from said common plane to said second plane, a plurality of spaced-apart support projections extending outwardly from at least said third and fourth side flanges, said projections having outer edges spaced outwardly from said third and fourth side flanges, and recesses formed in said projections intermediate said outer edges and said third and fourth side flanges, said recesses opening outwardly toward at least one of said first and second opposite faces of said grid member.
 5. The grid member of claim 4 wherein said recesses open outwardly toward both of said first and second opposite faces.
 6. The grid member of claim 4 and further including lateral extensions projecting laterally from said outer edges of said projections in substantially parallel relationship to said third and fourth side flanges. 